Dough To Pan Size Ratio

So this is really to try to answer my question of how do you work out how much dough you put in a tin.

My tins:

Large pan internal measurements = 28cm x 13cm x 6.5cm = nett water contained = 2250g

Small pan internal measurements =21cm x 11cm x 6.5cm = nett water contained = 1450g

So I looked at a number of posts and got some advice and I was very confused. I decided that I would bake a loaf to try to work the ratio should one exist.